U.S. Pat. No. 4,755,769 is directed to a power transmitter and conversion circuit for selecting output power from one or more of a plurality of power amplifiers. The patent uses shorting electromechanical switches and does not disclose the use of phase shifters to vary the output power.
U.S. Pat. No. 4,016,503 discloses an amplifier network which improves reliability through automatic passive switching between two parallel circuits, while providing a constant level of output power. The output power of the reference circuit is equal to only one-half the power of either of the two amplifiers. The summing of power levels of the constituent amplifiers is not disclosed.
U.S. Pat. No. 4,311,965 discloses a power switching technique for a multi-module amplifier where one or more modules may be disconnected without affecting the performance of the other modules. In a low power mode, a large amount of amplifier power is dissipated in the combining circuit. No use of phase shifting to facilitate switching is disclosed.
The instant invention is directed to the use of two parallel power amplifiers, such that the amplifiers may be used individually or in combination to increase the output power signal. The transmission and combination of signals is effected using phase mixing, thereby avoiding the weight and reliability problems of switches. None of the prior art now known and described above, either alone or in combination, solves these problems.